A track-and-hold circuit (T/H) may be used to sample and condition analog signals. A T/H is often used at the front end of analog-to-digital converters (ADCs) to sample a signal and then hold the signal sample constant-such that conversion circuitry of the ADC has time to convert and process the sample. The T/H function typically involves high speed switching of analog signals. As a result, the T/H may often exhibit glitches in its output waveform, often referred to as acquisition glitches. The acquisition glitch, which occurs after the hold-to-track transition when the device is tracking and acquiring the signal, tends to be the dominant glitch or perturbation in the output waveform of a switched T/H, such as a switched emitter follower (SEF) T/H, a diode bridge switched T/H, or similar type switched T/H. The acquisition glitch is typically impulsive and has very high energy and very short time duration. This may tend to excite any ringing responses that may be present in the signal path or the input circuit of the downstream ADCs often used with a T/H. The acquisition glitch may cause input level compatibility problems in ADCs. The ringing/settling time associated with the response of the ADCs to the glitch can slow down the permissible sample rate and degrade conversion accuracy.
It is therefore desirable to achieve a T/H design with minimized glitch amplitude, particularly in high speed applications where sampling bandwidths extend to several GHz and ringing phenomena can be difficult to control due to sensitivity to small parasitic elements.